1. Field of the Invention
This present invention relates to magnetic disk storage systems, and more particularly, to a high reliability high performance hard disk drive systems having a unique structural organization, which includes special focus on isolating the disk area to four quadrants-based on the Cartesian system of coordinates- and read/write functions thereof with respect to timing. Out of which it has concurrent access to two quadrants and both sides of a disk in an instant in time. System has two pairs of actuator-carriage arms with multiple read/write head/disk interface regions, which regions offer greatly enhanced performance regardless of system size (i.e., media form factor). Continuous micro-pad contact and low fly height read and write and the use therefore of a low-mass, low fly height head/structure-suspension (both integrated as a single unit,) are key contributors at this interface regions. The invention can be used in any size rigid-disk system (size independence) that enables application of the invention for all small-media-form-factors as well. The number of platters can be increased to three or four or more.
2. Description of the Prior Art
Magnetic hard disk drives are used as the primary storage devices for a wide range of applications, including desktop, mobile and server systems. Demand for disk storage is increasing 60%–70% per year on a worldwide basis. In near future, consumer electronics and computer games and other media applications are very likely to form the basis for additional demand growth facing the disk drive industry.
A typical hard disk drive is made of a stack of closely spaced rigid disks, with actuator arms that carry very small magnetic transducer heads that move radially within the said stack of disks in a comb-like manner.
Since certain form factors have become standard in the industry, hard disk drive systems must be compatible to sizes of these form factors. Therefore, based on this constraint, increases in memory capacity of a hard disk drive of a given standard size are possible either by increasing the density of data written on a given area of a disk or by improving mechanical design. The trend has been towards smaller form factors.
The technologies involved in magnetic storage products generally are in one of the following categories: a) Technologies that pertain to the geometric formation of the heads for the contacting or non-contacting way of operation. b) Technologies that pertain to the design of the head/disk assembly that serves the operation of the read/recording heads, c) Technologies that pertain to the control and recording electronics, d) Technologies that pertain to the composition of the magnetic coating and lubricants.
Among the most important disk drive performance measurements are: a) Formatted box storage capacity, it measures storage capacity per unit of volume and has increasingly become more important as space is limited in desktops, and especially notebooks, laptops and other small portables; b) average access time to data, it is very important as it determines the time required to locate or store data and, c) data transfer rate, it is important as the disk drive data transfer rate influences overall system performance.
Reliability is the number one priority for users, number two priority is cost, but improved access time is also important-despite already improved fast seek times achieved. Therefore, different magnetic head positioning-actuator arms and drive arrangements have been designed to achieve such improvements, besides increasing the number of the disks.
Prior art magnetic positioning mechanisms-actuator arms developed are of two main type. Linear positioners are made of a carriage to carry actuator arms that are moved radially relative to the axis of the rotation of the disk to position the magnetic heads along multiple circumferentially positioned tracks. Pivotal actuator arms pivot on an axis parallel to the axis of the disks, thereby magnetic heads are carried at the ends of the arms and move in arcuate paths over the magnetic tracks of the disks. Current commercial hard disk systems employ mostly a conventional planar moving coil actuator assembly.
Prior art moving coil actuator assembly consists of an analog voice coil, a carriage arm, a suspension and head gimbal assembly member and a pivot member. The electro-magnetic actuation force F.sub.A becomes effective at one end of the carriage arm in order to actuate the head positioning assembly. This results in a reaction force F.sub.P that is effective on the pivot member, since the force F.sub.A is a non-coupled force. The reaction force F.sub.P causes a vibrartion on the actuator assembly at about the pivot member, usually in a track seeking direction. This Quasi-Rigid body vibration mode is at mid band of about 4.about.6 Khz. Conventional planar moving coil actuator assembly usually has a track density of 6000.about.8000 TPI. The head positioning of these systems have a cross over frequency of 500.about.700 Hz, that can be sufficient for only 12000.about.14000 TPI. Whereas, the increasing trend of higher TPI makes fine-precision head positioning even more important and critical.
The current state of the art read/write heads operate at a distance of the order of 0.1–0.5 micron above the disk surface. This height—as per straight arm actuator and suspension system—being a microscopic distance; a range of 0.000004 to 0.00002 inch of fly height, has the potential danger of head crashes and loss of data when for example an unexpected impact-shock occurs to the desktop or to the notebook as the system is running—and this causes the head to ding as it is called in the field, to the hard disk surface, or sudden power failures result in head crash, or damage to heads or to surface. Nevertheless, it is desirable to have a fly height as close to the recording media as possible.
The low fly height and increased recording density can be understood from the following first equation tat expresses the dependence of the length of a pulse width PW50 obtained from a recording transition an the recording system.PW50={g2+4(d+a)(d+a+.delta.)}.sup.½  (1)where    g=gap length of the recording head    d=the distance separating the head and media    a=2Mr.delta./Hc (length of a recording transition)    .delta.=film thickness    Mr.delta.=magnetization-thickness product    Hc=coercivityThis equation was provided by Williams and Comstock in “An Analytical Model of the Write Process in Digital Magnetic Recording, 17th Annual AIP Conference Proceedings, part 1, No. 5, 1971, pp. 738–742, American Institute of Physics.
Furthermore, disk tangential velocity is greater at outer tracks than at inner tracks that result in different wind speeds based upon where the slider is positioned. In rotary actuated drives, the slider changes skew angle from liner tracks to outer tracks. These differing wind speeds and differing skew angles cause variations in fly height.
Invention assumes zero disk slippage-therefore zero variation in track radius by runout and track distortion as a result of using high quality spindle and clamps.
Another problem with prior art hard disk drives is that at specific time intervals during normal operation of hard disk drive, a sequence called Servo Bank Write (SBW) is performed. At this time, write heads write position data to all of the servo wedges at the same time. In prior art hard disk drive systems, the sensitive read heads are subject to voltage variation in the SBW mode, where bias current can drop from I.sub.biastotal in the read mode to I.sub.biastotal/N in the SBW mode, that could result in read head damage. This problem is addressed by U.S. Pat. No. 6,594,101 entitled; Read Head Protection Circuit and Method, and can be implemented for the purposes of the present invention—it would be especially relevant, as a multiple number of read/write heads are employed in the present invention.
Furthermore, whenever the drive motor is turned on and off, the slider undergoes a sliding contact with a portion of the disk. This contact between the slider and the disk when the drive is turned on and off is known as contact start stop (CSS) operation. This CSS motion is a major cause that lowers reliability as the drive gets older and therefore reduces reliability in the long run. 20,000 CSS cycles for desk top and 100,000 CSS cycles for portable computer applications is considered proper. A higher number of CSS cycles is needed especially in systems where these are turned on and off frequently. A higher CSS number also means a longer product life expectancy and reliability.
Friction is related to two important problems: 1) Power consumption, 2) Head vibration. Lower power consumption is very important for battery-powered laptops, notebooks and portable systems. For these systems, power consumption due to interface should be a small fraction of 800 mW. With respect to friction sliding and stiction, these constraints are addressed by U.S. Pat. No. 5,949,612; entitled Low Friction Sliding Hard Disk Drive System, where the continuous sliding and the disk surface adhesion reduction texture that has a microscopic RMS roughness aspect that also reduces capillary adhesion, can be made compatible with minor adjustments and be applicable for the purposes of this invention. The friction must be minimized between the slider and the disk. Therefore, the solution of the invention to this problem is one continuous contact micro-pad per two thin film transducers.
Among various causes, the main cause of data loss is hard drive failures. The overall cause of data loss due to hard drive failures is a very high rate of 65%. For small and mid size companies, those that can not or have not made an investment in additional back up systems, data loss due to hard drive failures can mean great economic losses and may even result in business failures.
Among all hard drive failures, stiction accounts for about 60%. It is defined as the force it takes to get an object at rest on another object to start sliding. It is measured in grams to indicate the force required to separate the slider form the disk. The second type of stiction is called parking stiction and is a term used to indicate when the drive has not been in use and has been in the CSS zone. One reason of stiction is that some drives are lubricated with shellac or lacquer or other lubricants—when these get hot these liquefy. When drive is turned off, heads come to rest on the surface of CSS zone and the coating solidifies as the drive cools—and acts like a glue that keep the heads on the platter. Spindle failure accounts for about 15%, failed electronics on the drive account for about 20%.
The recovery services provided by data recovery companies for hard disk failures and to recover valuable data are very costly. Depending on the type of drive, it starts from $3,000 to $12,000 to recover data from a hard disk—if recoverable at all.
The straight-arm actuator system—which is a standard on most disk drives—is actually a system with inherently problematic structural and functional aspects.
First major problem is the limitation of the straight-arm actuator with respect to the disk area that it can cover simultaneously at any given instant in time. The straight-arm actuator can not cover different quarters of the disk concurrently at any given instant in time. Therefore, it must make many swinging motions-usually on one area arcuate trajectory to reach tracks that are located at many different concentric areas of the disk. Post boot up normal operational conditions, the single straight-arm actuator and similar variations of the same system have to make relatively long back and forth distance motions over the disk, as well.
Given the increased density of tracks, increased precision is needed. Despite the swift motions of the straight arm actuator, reaching the different tracks on the many different concentric areas of the disk is not instantaneous and requires many motions that involve sudden direction reversals of the straight-arm actuator that also have to be precise. The trajectory from the inner most tracks to the outer most tracks is a relatively long distance and as track densities increased, the precision demanded from the actuator system has been increasing substantially, since state of the art disks can have up to 20.000 tracks or more.
However, second, these motions of the straight-arm actuator and the associated read/write head assembly are subject to vibrations. Vibration has adverse effect on these small and sensitive components, including head vibration. Head vibration depends in part to mechanical resonance of slider—which generally increase with friction. Reduction of friction reduces both power consumption and head vibration.
Higher rpm is chosen as a way for fast access. However, this creates a third problem, high rpm has the problem of creating excess heat and is more demanding on the spindle motor. For example, state of the art 10,000 rpm drives reach a temperature of 100 F. and above during intensive use. Such a temperature is not tolerable in a cramped case without extra cooling. Additional cooling has both space and cost constraints. Furthermore, high rpm has more wear and tear-instability potential, especially in systems that are frequently turned on and off.
Fourth problem with any type of straight arm actuator system involves the constraint of having to park the R/W heads away from data tracks to a zone near the spindle, before the platter stops turning, because it depends on a microscopic distance of air cushion, that in turn depends on the turning of the disk that must not have any variation in the rpm during operation. When system is turned off or due to unexpected power failures for instance the constraint of having to park the heads come up. Parking the heads involves moving the read/write heads all the way to the parking zone—and to land heads, to a region that is located at the innermost reach of the head positioning system, each and every time the system is turned off. Then the heads must take off and then be moved back to data tracks when system is turned on.
Therefore, fifth, additionally because of microscopic fly height of the R/W heads, there is always the potential for damage to both R/W heads and damage to the substrate on the disk as the system is running—for example when the system is subject to external inadvertent shocks-bumps.
Sixth, these frequent motions also involve interruptions of reading or writing data streams. With a single straight-arm actuator, only serial data transfer scheme is possible. In serial data transfer scheme, the actuator first positions the R/W heads over a certain data track, then data is read or written with one head at a time then the data stream is interrupted as actuator moves heads to a different track. Due to frequent interruptions, the data transfer rate is much slower as compared to a parallel computing transfer scheme with continuous data stream.
These back and forth swings over a relatively long distance are erratic. This is especially true during the parking and boot up sequences, that are often repeated and hence in the long term, these sudden swings each time the system is started and turned off cause wear and tear. As a result, the system has lower reliability and lower product life expectancy.
Therefore, there is a need for an actuator mechanism that is: a) not subject to contact start stop (CSS) operation method and; b) not subject to Quasi-Rigid body vibrations and relatively high vibrations due to frequent direction reversals during the booting and parking, that is, there is need for an actuator system with lower-minimized vibration rates; c) based on concurrent access to more than one area of the disk surface at any given instant in time, by using more than one linear actuator and also because of a special geometric shape of the actuator-carriage arm that holds a plurality of R/W heads, it is able to read/write on multiple tracks, concurrently; d) not depended on high rpm that creates heat and/or is more demanding on spindle motor; e) Based on a constant R/W head low fly height that always remains at the same-constant fly-height-without the parking of R/W heads, with thin film R/W heads that have reduced interface surface; and f) based on an uninterrupted data transfer scheme—as in parallel data transfer scheme.